Centrifuge-based step emulsification device for simple and fast generation of monodisperse picoliter droplets

Monodisperse picoliter droplets have been widely used for biochemical reactors and preparation of functional microbeads for food, cosmetics, and medical industry. Although conventional microfluidic technologies enable the production of monodisperse picoliter droplets, special instruments (e.g. syringe pump) are required, leading to its poor usability and accessibility in other research fields. In this study, we propose centrifuge-based step emulsification device housed in a microtube for simple and fast generation of monodisperse picoliter droplets. Our device consists of a reservoir part for storage of the dispersed phase and a microchannel part for droplet formation. Centrifugation using a commercial centrifuge exerts excessive pressure on the dispersed phase, infusing it into a microchannel. The infused dispersed phase is pinched off, forming droplets due to the channel geometry for step emulsification. The produced droplets at the step then are transported to the bottom of the microtube due to the centrifugal force. Using this device, we achieved formation of monodisperse water-in-oil (W/O) picoliter droplets with diameters ranging from 18 to 90 μm. Moreover, we demonstrated the cell-free protein synthesis reaction in monodisperse picoliter droplets as well as the production of cell-sized glucose-responsive hydrogel microbeads. We believe that our device would be a powerful tool for simple and fast preparation of picoliter samples with high usability.